Microelectromechanical systems (MEMS) are presently in development for a variety of applications. MEMS provide three-dimensional circuits and mechanical components to a degree of miniaturization not possible previously. Of particular interest are MEMS micromirrors, which use piezoelectric layers to position an array of mirrors to provide optical switching, beam-forming and other functions. The individual mirrors may be positioned independently, and large arrays of mirrors may be incorporated on a single die.
Large dies such as are used to implement a micromirror array are difficult to mount on an integrated circuit substrate. Typically, an adhesive such as epoxy is used to bond a die to the substrate. However, epoxy and other bonding materials change shape during bonding and curing, so that the tilt and position of the die vary during fabrication and may ultimately deviate from the desired alignment. The ultimate tilt of the die, as well as the ultimate horizontal placement on the substrate affect the alignment of the array and thus the performance of the circuit in a larger system.
Smaller dies are more easily fabricated and placed than large dies, but the relative placement of multiple dies is not controllable with current processes to the degree of accuracy required. Since the mirrors in a micromirror array must be positioned relative to each other within very close tolerances, current processes dictate that the micromirror array be fabricated on a single die. Use of smaller dies would be desirable, as yields from a smaller die fabrication would be greatly improved.
Therefore, it would be desirable to provide a method and apparatus implementing a micromirror array, in which the position of the array on the substrate may be precisely controlled. It would further be desirable to provide a method and apparatus implementing an integrated circuit wherein a plurality of dies may be accurately positioned relative to each other on a substrate.